You can only lead people where they really want to go. Most "leaders" that I've seen see where the people are going, jump out in front, and yell "Follow me!"

A former neighbor of mine grew up in France during the German occupation. Her family suffered a great deal during that time including having some of them executed. She still doesn't like Germans. That's a far cry from actively attacking them, though.

I think Europe took the steps to peace after WWII because they'd learned some bitter lessons. The leaders and most of the adult population after the WWII had survived two world wars in their lifetime and didn't want to see a third. The hostility after WWI that led to the Treaty of Versailles was a major factor in Hitler's rise to power. It was necessary to put the hatred aside after WWII and build something positive. Individuals continued with their grudges but nations had to learn to go beyond them.

I believe quite a few heads of state and other leaders play the history card as a means of manipulating people. It works very well for demogagues. We see it here in America with some of our racial problems. Better to blame your problems on history (racism, slavery, etc.) than to accept the hard reality that some wounds are self-inflicted.

I doubt we'll see Turkey admit the Armenian genocide anytime soon. I doubt most people in the Balkans are going to wake up one day and realize that feuding over something that happened 500 years ago is absurd. I also believe that the only way we're likely to see "peace" in the Middle East any time soon is if Israel ceases to exist, and I don't think Israel is going to let that happen without a fight.

So, what can we do? Honestly, the only thing that comes to mind at the moment is what I mentioned before in response to your original post - to prevent the spread of these ancient hatreds to our countries, we're going to have to come down hard on anyone who brings them to our countries and commits violence. Failure to do so will likely result in all of us being caught in the crossfire.